Digital signal processor for audio, in-vehicle audio system and electronic apparatus including the same

ABSTRACT

A digital signal processor for audio includes: an interface circuit communicating with an microcomputer; a multi-band equalizer including digital filters corresponding respectively to bands, wherein the frequency characteristic of each digital filter is changed according to coefficient group; a memory; and a coefficient setting circuit setting the coefficient group of each digital filter, wherein the frequency characteristic of the multi-band equalizer is selected from presets, wherein, when the digital signal processor start, the interface circuit receives setting data corresponding to the presets from the microcomputer and stores the received setting data in the memory, and wherein, at the time of audio reproduction, the interface circuit receives selection data to designate one of the plurality of presets and the coefficient setting circuit sets the coefficient group of each digital filter according to one of the setting data stored in the memory, the one setting data corresponding to the selection data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2016-003685, filed on Jan. 12, 2016, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a digital signal processor for audio.

BACKGROUND

Audio equipment used for in-vehicle audio (car audio), home audio,portable audio and the like as a function of changing the frequencycharacteristic of the audio signal. For example, in a car audio product(or AV amplifier device), a user can select one from a plurality ofequalizer settings corresponding to audio genres and musical instrumentssuch as flat, rock, pops, vocals, piano, jazz, classical, etc. (presetequalizer) according to the user's preference. Alternatively, some caraudio products have a function of reproducing spaces such as concerthalls, jazz clubs, churches and the like (acoustic adjustment function).As another alternative, some car audio products have a function ofcorrecting the frequency characteristic and phase characteristic of anaudio signal reproduced from a speaker in accordance with a room soundfield so as to obtain the optimal frequency characteristic and phasecharacteristic at a viewing position (also referred to as fixedequalizer or room correction). These are collectively referred to asfrequency correction in this specification.

When such frequency correction is implemented by an analog circuit, thecircuit scale becomes enormous. Therefore, a digital signal processor(DSP) is used to perform digital signal processing on a digital audiosignal. FIG. 1 is a block diagram of an audio system including a DSP.The audio system 100 includes sound source 102, an analog amplifier 104,an A/D converter 106, a microcomputer 108, a DSP 110, a D/A converter112, a volume circuit 114, a power amplifier 116 and an electroacoustictransducer 118.

The sound source 102 is a CD player, a DVD player, a silicon audioplayer, a smart phone or the like and outputs an analog audio signal.The analog amplifier 104 amplifies the analog audio signal from thesound source 102 and matches the amplified analog audio signal with aninput range of the A/D converter 106 at the subsequent stage.Alternatively, a digital audio signal generated by the sound source 102may be directly input to the DSP 110.

The DSP 110 receives a digital audio signal from the A/D converter 106or the sound source 102 and performs a predetermined digital signalprocessing on the received digital audio signal. Examples of the signalprocessing by the DSP 110 may include stereo-monaural conversion,digital volume control and the like in addition to the above-describedprocessing related to frequency correction.

The D/A converter 112 converts the digital audio signal processed by theDSP 110 into an analog audio signal. The volume circuit 114 amplifies anoutput signal of the D/A converter 112 with a gain corresponding to avolume value. The power amplifier 116 amplifies an output of the volumecircuit 114 and drives the electroacoustic transducer 118 such as aspeaker or a headphone.

The microcomputer 108 integrally controls the audio system 100. Themicrocomputer 108 receives a command input by a user through a userinterface such as a volume button or a touch panel, and controls the DSP110 based on the command. The microcomputer 108 and the DSP 110 areinterconnected via a bus or a control line. For example, upon detectinga volume change instruction input by the user, the microcomputer 108transmits a command value of the gain of a digital volume circuit of theDSP 110 to the DSP 110.

FIGS. 2A and 2B are block diagrams related to the frequency correctionof the DSP 110. As shown in FIG. 2A, the DSP 110 includes a multi-bandequalizer 120 and an interface circuit 130 with the microcomputer 108.The multi-band equalizer 120 includes a plurality of M filters 122_1 to122_M corresponding to the number of bands M. Upon detecting anequalizer change instruction input by the user, the microcomputer 108transmits setting data of the filters 122_1 to 122_M.

FIG. 2B is a circuit diagram of the filter 122. This filter 122 is asecond-order IIR (Infinite Impulse Response) filter, and its Q value,frequency f and gain can be set by a combination of five coefficients b₀to b₂, a₀ and a₁.

The interface circuit 130 is, for example, an I²C (Inter IC) serialinterface and can transmit data with 8 bits as one word. In a case whereeach coefficient is 24 bits (or 32 bits), in order to transmit fivecoefficients, it is necessary to transmit data of 24×5/8=15 times perband and, for M=13 bands, data transmission of 13×15=195 times isrequired.

Various data are always transmitted/received between the microcomputer108 and the interface circuit 130. As one example, the audio system 100has a function (spectrum analyzer function) for visually displaying thefrequency spectrum of an audio signal being reproduced, and, during thereproduction of the audio signal, the microcomputer 108 reads out thesignal strength of each band via the interface circuit 130 of the DSP110. When data transmission for changing the setting of the equalizer isinterrupted, data transmission for the spectrum analyzer is stopped eachtime, so that the correct frequency spectrum is not displayed.Particularly with the I²C interface, it is necessary to wait for anacknowledgment ACK after sending data from a master to a slave, whichmay cause an overhead.

SUMMARY

The present disclosure provides some embodiments of a digital signalprocessor for audio, which is capable of reducing the data amount andnumber of data transmission between a microcomputer and a DSP duringaudio reproduction.

According to one embodiment of the present disclosure, there is provideda digital signal processor for audio, including: an interface circuitconfigured to communicate with an external microcomputer; a multi-bandequalizer which includes a plurality of digital filters correspondingrespectively to a plurality of bands, wherein the frequencycharacteristic of each of the digital filters can be changed accordingto a coefficient group; a memory; and a coefficient setting circuitconfigured to set the coefficient group of each of the digital filters.The frequency characteristic of the multi-band equalizer can be selectedfrom a plurality of presets. At the time of start of the digital signalprocessor, the interface circuit receives a plurality of setting datacorresponding respectively to the plurality of presets from themicrocomputer and stores the received plurality of setting data in thememory. At the time of audio reproduction, the interface circuitreceives selection data to designate one of the plurality of presets andthe coefficient setting circuit sets the coefficient group of each ofthe plurality of digital filters according to one of the plurality ofsetting data stored in the memory, the one setting data corresponding tothe selection data.

All of the setting data corresponding respectively to the plurality ofpresets are transmitted from the microcomputer to the DSP at the time ofstart of the system and only the selection data is transmitted duringaudio reproduction. This makes it possible to reduce the data amount andnumber of data transmission during audio reproduction.

The setting data may include the coefficient group of each of theplurality of digital filters.

A frequency of each of the plurality of bands may be fixed, and thesetting data may include a gain of each of the plurality of bands. Thecoefficient setting circuit may hold the correspondence between the gainand a coefficient group of the corresponding digital filter for each ofthe plurality of bands.

The digital signal processor may further include: a delay circuit whichis disposed before or after the multi-band equalizer and is configuredto provide a variable delay to an audio signal. The setting data mayinclude a plurality of delay setting values corresponding respectivelyto the plurality of presets. At the time of audio reproduction, thecoefficient setting circuit may set a delay amount of the delay circuitaccording to the delay setting values included in one of the pluralityof setting data stored in the memory, the one setting data correspondingto the selection data.

With this configuration, it is possible to support presets usingreverberation.

The digital signal processor may be integrated on a single semiconductorsubstrate.

As used herein, the term “integrated” is intended to include both of acase where all elements of a circuit are formed on a semiconductorsubstrate and a case where main elements of the circuit are integratedon the semiconductor substrate. In addition, some resistors, capacitorsand the like for adjustment of a circuit constant may be providedoutside the semiconductor substrate.

According to another embodiment of the present disclosure, there isprovided an in-vehicle audio system including the above-describeddigital signal processor.

According to another embodiment of the present disclosure, there isprovided an electronic apparatus including the above-described digitalsignal processor.

Any combinations of the above-described elements or changes of therepresentations or the elements of the present disclosure betweenmethods, apparatuses and systems are effective as embodiments of thepresent disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an audio system including a DSP.

FIGS. 2A and 2B are block diagrams related to the frequency correctionof the DSP.

FIG. 3 is a block diagram of a DSP according to a first embodiment.

FIG. 4 is a view showing one example of setting data.

FIG. 5 is a sequence diagram of an audio system including a DSP.

FIG. 6A is a view showing another example of the setting data.

FIG. 6B is a table showing the correspondence between a gain g and acoefficient group of a first band.

FIG. 7 is a block diagram of a DSP according to a third embodiment.

FIGS. 8A and 8B are views showing one example of setting data.

FIG. 9 is a block diagram showing the configuration of an in-vehicleaudio system including a DSP.

FIGS. 10A to 10C are external views of electronic apparatuses.

DETAILED DESCRIPTION

Preferred embodiments of the present invention will now be described indetail with reference to the drawings. Throughout the drawings, the sameor similar elements, members and processes are denoted by the samereference numerals and explanation of which will not be repeated. Thedisclosed embodiments are provided for the purpose of illustration, notlimitation, of the present disclosure and all features and combinationsthereof described in the embodiments cannot be necessarily construed todescribe the spirit of the present disclosure.

In the specification, the phrase “connection of a member A and a memberB” is intended to include direct physical connection of the member A andthe member B as well as indirect connection thereof via other member aslong as the other member has no substantial effect on the electricalconnection of the member A and the member B. Similarly, the phrase“interposition of a member C between a member A and a member B” isintended to include direct connection of the member A and the member Cor direct connection of the member B and the member C as well asindirect connection thereof via other member as long as the other memberhas no substantial effect on the electrical connection of the member A,the member B and the member C.

First Embodiment

FIG. 3 is a block diagram of a DSP 200 according to a first embodiment.The DSP 200 performs various signal processing on a digital audiosignal. For example, the DSP 200 can be used as the DSP 110 in the audiosystem 100 of FIG. 1.

The DSP 200 can change the frequency characteristic of the audio signalunder control of an external microcomputer 108. The DSP 200 includes aninterface circuit 202, a memory 204, a coefficient setting circuit 206and a multi-band equalizer 220. The interface circuit 202 communicateswith the external microcomputer 108. For example, the interface circuit202 may be an I²C interface.

The multi-band equalizer 220 includes a plurality of digital filters222_1 to 222_M corresponding to a plurality of M (M being an integer of2 or more) bands BAND1 to BANDM. The frequency characteristic of eachdigital filter 222 can be changed according to a coefficient group. Thedigital filter 222 may be either an IIR (Infinite Impulse Response)filter or a FIR (Finite Impulse Response) filter. An adder 224 addsoutputs of the plurality of M digital filters 222_1 to 222_M. Theconfiguration of the multi-band equalizer 220 is not limited to thatshown in FIG. 3. For example, the plurality of digital filters 222 maybe connected in series. Alternatively, the multi-band equalizer 220 maybe configured by a combination of serial connection and parallelconnection of the plurality of digital filters 222.

The coefficient setting circuit 206 sets a coefficient group of each ofthe plurality of digital filters 222_1 to 222_M. For example, when thedigital filters 222 are the second-order IIR filters in FIG. 2B, thecoefficient group includes five coefficients b₀ to b₂, a₁ and a₂.

The frequency characteristic of the multi-band equalizer 220 can beselected from a plurality of N (N being an integer of 2 or more)frequency characteristics (hereinafter referred to as “presets”). Forexample, a plurality of presets are prepared for each audio genre andmusical instrument, such as flat, rock, pops, vocal, piano, jazz,classic, etc. Alternatively, the plurality of presets may be preparedfor acoustic adjustment functions to reproduce reverberation of concertalls, jazz clubs, churches, etc. These presets may also containcomponents of equalization for room correction.

At the time of start of the DSP 200, the interface circuit 202 receivesa plurality of setting data S₁ to S_(N) corresponding respectively tothe plurality of presets from the microcomputer 108 and stores them inthe memory 204.

Then, at the time of audio reproduction, the interface circuit 202receives selection data SEL to designate one of the plurality ofpresets. The coefficient setting circuit 206 sets the coefficient groupof each of the plurality of digital filters 222_1 to 222_M according toone of the plurality of setting data S₁ to S_(N) stored in the memory204, which corresponds to the selection data SEL.

FIG. 4 is a view showing one example of the setting data. For example,the setting data S₁ may include a plurality of coefficient groupscorresponding to the plurality of bands BAND1 to BANDM (that is, theplurality of digital filters 222). This is equally applied to othersetting data S₂ to S_(N).

Assume that a selection signal SEL to instruct an i^(th) (1≦i≦N) presetis written in the memory 204 during audio reproduction. At this time,the coefficient setting circuit 206 refers to i^(th) setting data S_(i)and sets a coefficient group of each hand included therein to thedigital filter 222 of the corresponding band.

The above is the configuration of e DSP 200. Subsequently, the operationthereof will be described. FIG. 5 is a sequence diagram of the audiosystem 100 including the DSP 200. Immediately after startup, a setupsequence S100 is executed. In the setup sequence S100, N setting data S₁to S_(N) corresponding respectively to the plurality of N presets aretransmitted from the microcomputer 108 to the DSP 200 (S102). Thistransmission is a scheduled processing, not an interrupt processing. Theinterface circuit 202 of the DSP 200 stores the received N setting dataS₁ to S_(N) in the memory 204.

After completing the setup sequence, the microcomputer 108 initializesthe coefficient groups of the plurality of digital filters 222 beforeproceeding to a reproduction sequence S110. For example, the DSP 200holds an initial value (default value) of the preset and may initializethe multi-band equalizer 220 according to the initial value.Alternatively, the microcomputer 108 may transmit the initial value ofthe preset, as the selection data SEL, to the DSP 200 during the setupsequence.

Upon the completion of the setup sequence S100, the process proceeds tothe reproduction sequence S110. During the reproduction sequence S110,the DSP 200 performs various signal processing (not shown in thesequence diagram of FIG. 5) on an audio signal. Further, during thereproduction sequence S110, the microcomputer 108 exchanges various data(not shown in the sequence diagram) with the DSP 200. For example, thisexchange includes data transmission for spectrum analyzer function.

When the microcomputer 108 detects an input of change of the preset by auser during the reproduction sequence S110 (S112), the microcomputer 108transmits the selection data SEL to designate the changed preset to theDSP 200 (S114).

The coefficient setting circuit 206 of the DSP 200 selects setting dataS_(i) corresponding to the preset designated by the selection data SEL(S116) and sets a coefficient group corresponding to the selectedsetting data S_(i) in the digital filter 222 (S118). Thereafter, whenthe change of the equalizer is instructed again, the operations of S112to S118 are performed.

The above is the operation of the audio system 100 including the DSP200. According to the DSP 200, during the setup sequence, the settingdata S₁ to S_(N) corresponding to all the presets are transmitted and,during the audio reproduction, only the selection data SEL to designatethe preset is transmitted. For example, when N (=8) presets areselectable, the selection data SEL may be 3 bits, so, when there is achange in the preset equalizer during audio reproduction, the preset canbe switched with data transmission only once.

In contrast, in the setup sequence S100, the setting data S₁ to S_(N)corresponding to all the presets are transmitted. As shown in FIG. 4, itis assumed that each setting data S includes a coefficient group foreach band. In a system where a coefficient group contains 5coefficients, each of which is 24 bits and M=13 bands, data of 12480bits (=5×24 bits×M×N=5×24×13×8) are transmitted in the setup sequenceS100. In a 1-word 8-bit serial interface, 1560 data transmissions occur.However, the data transmission in the setup sequence S100 is a scheduledprocessing rather than an interrupt processing. Therefore, this datatransmission does not interfere with other data transmission and doesnot become a bottleneck of the processing of the DSP 200 or themicrocomputer 108. In addition, since it is not necessary to considerthe interrupt processing, the burden of software design is greatlyreduced.

Second Embodiment

In the first embodiment, the frequencies of the plurality of bands BAND1 to BANDM in the multi-band equalizer 220 are variable. Such anequalizer is also called a parametric equalizer. In a second embodiment,the frequency of each band is fixed. Such an equalizer is also called agraphic equalizer. For example, the frequencies of multiple bands arespecified in the unit of octave. Then, in the multi-band equalizer 220,only the gain of each band is variable. FIG. 6A is a view showinganother example of the setting data. The setting data S₁ in FIG. 6Aincludes the gains g₁ to g_(M) of the respective bands BAND1 to BANDM.This is equally applied to other setting data S₂ to S_(N).

The coefficient setting circuit 206 holds the correspondence between again g and a coefficient group of the corresponding digital filter 222for each of the plurality of bands BAND 1 to BANDM. FIG. 6B is a tableshowing the correspondence between the gain g and the coefficient groupof the first band BAND1. For example, a value of the gain g can beselected from 15 levels in the unit of 1 dB between −7 dB and +7 dB. Agroup of coefficients b₀ to b₂, a₀ and a₁ is held for each gain value.The specific values of the coefficients are omitted. This is equallyapplied to the other bands BAND2 to BANDM. The correspondence shown inFIG. 6B may be held as a table or may be held by an operationalexpression.

When the gain of each band can be set in 15 steps, the setting of thegain is 4 bits. According to the second embodiment, the setting data S₁to S_(N) transmitted in the setup sequence S100 are 416 bits (=4bits×M×N=4×13×8). Therefore, when the 1-word 8-bit serial interface isused, data transmission of 52 times suffices, which is considerablyreduced as compared with the first embodiment.

It may be said that the second embodiment is suitable for applicationswhere the number of bands M is as large as 10 or more, whereas the firstembodiment is suitable for applications where the number of bands M is10 or less (or the number of bands M may be 5 or less).

Third Embodiment

FIG. 7 is a block diagram of a DSP 200 a according to a thirdembodiment. The DSP 200 a is composed of, for example, two channels (Lchannel and R channel) which have multi-band equalizers 220L and 220R,respectively. Here, the DSP 200 a is illustrated with a DSP forin-vehicle audio. An in-vehicle audio system has a total of 4 speakers,i.e., front left, front right, rear left and rear right. An output ofthe multi-band equalizer 220L is distributed to the front left and rearleft speakers and an output of the multi-band equalizer 220R isdistributed to the front right and rear right speakers.

The DSP 200 a further includes delay circuits 230FL, 230RL, 230FR and230 RR. These delay circuits 230 are variable delay circuits whose delayamount can be independently adjusted according to a delay setting value.

Although it is shown in FIG. 7, for the purpose of clarity, that onemulti-band equalizer 220 is shared between the front and rear in each ofthe L channel and the R channel, the present disclosure is not limitedthereto. In other words, the multi-band equalizer 220 may be providedindividually for each of the front and rear, and therefore, themulti-band equalizer 220 may be provided for each speaker. This makes itpossible to set a sound field with overflowing presence. Alternatively,only one common multi-band equalizer may be provided for all channels.As another alternative, one multi-band equalizer 220 shared by the frontchannel and the front R channel and one multi-band equalizer 220 sharedby the rear L channel and the rear R channel may be provided.

FIGS. 8A and 8B are views showing one example of setting data. Settingdata S₁ includes delay setting values D_(FL), D_(RL), D_(FR) and D_(RR)for the plurality of delay circuits 230F 230RL, 230FR and 230RR,respectively, in addition to data for the multi-band equalizer 220. Thesetting data S₁ of FIG. 8A includes data for the multi-band equalizer220 in the format of FIG. 4. The setting data S₁ of FIG. 8B includes thedata for the multi-hand equalizer 220 in the format of FIG. 6A. Inaddition, in FIG. 7, when different frequency characteristics are setfor the multi-band equalizer 220L and the multi-band equalizer 220R forthe same preset, data for the multi-band equalizer 220L of the L channeland data for the multi-band equalizer 220R of the R channel may beincluded in the setting data S₁.

Subsequently, the operation of the DSP 200 a will be described. In thesetup sequence, the interface circuit 202 receives a plurality ofsetting data S₁ to S_(N) corresponding respectively to a plurality ofpresets and holds them in the memory 204. When the interface circuit 202receives the selection data SEL to designate a preset, the coefficientsetting circuit 206 selects one setting data S_(i) corresponding to theselection data SEL and sets the frequency characteristics of themulti-band equalizers 220L and 220R and the delay amounts of the delaycircuits 230FL, 230RL, 230FR and 230RR based on the selected settingdata S_(i).

The above is the configuration and operation of the DSP 200 a accordingto the third embodiment. According to the DSP 200 a, it is possible toinstantaneously switch a preset using a delay. For example, a presetrelated to a sound adjustment function can use a reverberation effect bydelaying a sound from the rear speaker relative to a sound from thefront speaker. According to the third embodiment, since the delay amountcan be switched for each preset, it is possible to support presetsrelated to acoustic adjustment and the like.

Alternatively, in car audio, distances between a viewing position (forexample, a driver's seat) and four speakers are different from eachother, and, when the speakers sound with the same phase, the phasesthereof are shifted at the viewing position and a sound image isblurred. In room correction (also called a sound field correction or afixed eraser) for correcting this, it is necessary to set differentdelay amounts for different speakers. According to the third embodiment,it is possible to select a preset in consideration of room correction.

APPLICABILITY

Finally, applications of the DSP 200 will be described. FIG. 9 is ablock diagram showing the configuration of an in-vehicle audio system500 including the DSP 200. The in-vehicle audio system 500 is composedof four channels (front right FR, rear right RR, front left FL and rearleft RL) and has a plurality of speakers 502FR, 502RR, 502FL and 502RLcorresponding respectively to the four channels. The in-vehicle audiosystem 500 may be a 5.1 channel system further including a centerchannel and a subwoofer channel.

A sound source 504 is a CD player, a DVD player, a Blu-ray player, anHDD/silicon audio player, a radio tuner or the like and reproducesanalog or digital audio signals. The DSP 200 receives an audio signalfrom the sound source 504 and performs various digital signal processingon the received audio signal. The audio signal subjected to theprocessing of the DSP 200 is converted into an analog audio signal whichis then input to an amplifier 506. The amplifier 506 amplifies theanalog audio signal of each channel and drives the corresponding speaker502. The microcomputer 108 integrally controls the blocks including theDSP 200. The sound source 504, the microcomputer 108, the DSP 200 andthe amplifier 506 operate with power supplied from a battery 508. Thesound source 504, the microcomputer 108, the DSP 200 and the amplifier506 may be incorporated in a head unit 510. In addition, the amplifier506 may be integrated on the same chip as the DSP 200.

When a user (driver) turns on an ignition (or accessory on), power issupplied to circuits including the microcomputer 108. When the power issupplied, the process proceeds to the setup sequence and the settingdata S₁ to S_(N) are transmitted from the microcomputer 108 to the DSP200.

The DSP 200 may also be mounted on electronic apparatuses such as anaudio component device, a television, a desktop PC, a notebook PC, atablet PC, a mobile phone terminal, a digital camera, a portable audioplayer, etc. in addition to the above-described in-vehicle audio system.

FIGS. 10A to 10C are external views of electronic apparatuses. FIG. 10Ashows a display 600 which is one example electronic apparatus. Thedisplay 600 includes a housing 602 and a speaker 612. The DSP 200 isincorporated in the housing 602.

FIG. 10B shows an audio component device 700 which is one example of anelectronic apparatus. The audio component device 700 includes a housing702 and speaker 712. The DSP 200 is incorporated in the housing 702.

FIG. 10C shows a small information terminal 800 which is one example ofan electronic apparatus. The small information terminal 800 is a mobilephone, a tablet terminal, an audio player, or the like. The smallinformation terminal 800 includes a housing 802, a speaker 812 and adisplay 804. The DSP 20 is incorporated in the housing 802.

According to the present disclosure in some embodiments, it is possibleto reduce the data amount of data transmission between a microcomputerand a DSP during audio reproduction.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosures. Indeed, the novel methods and apparatusesdescribed herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe embodiments described herein may be made without departing from thespirit of the disclosures. The accompanying claims and their equivalentsare intended to cover such forms or modifications as would fall withinthe scope and spirit of the disclosures.

What is claimed is:
 1. A digital signal processor for audio, comprising:an interface circuit configured to communicate with an externalmicrocomputer; a multi-band equalizer which includes a plurality ofdigital filters corresponding respectively to a plurality of bands,wherein the frequency characteristic of each of the digital filters ischanged according to a coefficient group; a memory; and a coefficientsetting circuit configured to set the coefficient group of each of thedigital filters, wherein the frequency characteristic of the multi-bandequalizer is selected from a plurality of presets, wherein, at the timeof start of the digital signal processor, the interface circuit receivesa plurality of setting data corresponding respectively to the pluralityof presets from the microcomputer and stores the received plurality ofsetting data in the memory, and wherein, at the time of audioreproduction, the interface circuit receives selection data to designateone of the plurality of presets and the coefficient setting circuit setsthe coefficient group of each of the plurality of digital filtersaccording to one of the plurality of setting data stored in the memory,the one setting data corresponding to the selection data.
 2. The digitalsignal processor of claim 1, wherein the setting data includes thecoefficient group of each of the plurality of digital filters.
 3. Thedigital signal processor of claim 1, wherein a frequency of each of theplurality of bands is fixed, wherein the setting data includes a gain ofeach of the plurality of bands, and wherein the coefficient settingcircuit holds the correspondence between the gain and a coefficientgroup of the corresponding digital filter for each of the plurality ofbands.
 4. The digital signal processor of claim 1, further comprising: adelay circuit which is disposed before or after the multi-band equalizerand is configured to provide a variable delay to an audio signal,wherein the setting data includes a plurality of delay setting valuescorresponding respectively to the plurality of presets, and wherein, atthe time of audio reproduction, the coefficient setting circuit sets adelay amount of the delay circuit according to the delay setting valuesincluded in one setting data of the plurality of setting data stored inthe memory, the one setting data corresponding to the selection data. 5.The digital signal processor of claim 1, wherein the digital signalprocessor is integrated on a single semiconductor substrate.
 6. Anin-vehicle audio system comprising a digital signal processor ofclaim
 1. 7. An electronic apparatus comprising a digital signalprocessor of claim 1.